Electro-optical device and method for driving the same

ABSTRACT

A novel structure of an active electro-optical device is disclosed. The device is provided with complementary thin film insulated gate field affect transistors (TFTs) therein which comprise a P-TFT and an N-TFT. P-TFT and N-TFT are connected to a common signal line by the gate electrodes thereof, while the source (or drain) electrodes thereof are connected to a common signal line as well as to one of the picture element electrodes. In case of driving the active electro-optical device, a gradation display can be carried out in a driving method having a display timing determined in relation to a time F for writing one screen and a time (t) for writing in one picture element, by applying a reference signal in a cycle of the time (t), to the signal line used for a certain picture element driving selection, and by applying the select signal to the other signal line at a certain timing within the time (t), and whereby setting the value of the voltage to be applied to a liquid crystal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electro-optical device, e.g. to anactive liquid crystal electro-optical device, in particular, to a deviceprovided with two complementary thin film insulated gate field effecttransistors (hereinafter referred to as C/TFTs) having a structure ofmodified transfer gate MTG).

Also, the present invention relates to a method for driving an activeelectro-optical device, in particular, to a method for driving an activeelectro-optical device with clear gradation level in a digital mode.

2. Description of the Prior Art

An active liquid crystal electro-optical device utilizing TFT isconventionally know. In this device, an amorphous or polycrystallinesemiconductor is used for TFT, while either one of conductive type aloneis used for each picture element thereof. Namely, an N-channel TFT(referred to as NTFT) is generally linked to the picture element inseries.

Since the dielectric constant in a direction parallel to a molecularaxis of the liquid crystal composition provided between substrates isdifferent from that in a direction perpendicular thereto due to thematerial property thereof, arrangement of the composition con easily bemade in both directions, horizontally or vertically, to the outsideelectric field. By utilizing the anisotropy of dielectric constant, theamount of transmitted light or of dispersion thereof is controlled in aliquid crystal electro-optical device, so as to perform on/off display.

FIG. 3 shows an electro-optic property of nematic liquid crystal. Whenthe applied voltage is small, which is indicated by Va or a point A, theamount of transmitted light is approximately 0%, and at Vb or point B,it is approximately 20%, while at Vc or point C, it is approximately70%, and at Vd or point D, it amounts to approximately 100%. Therefore,when the points A and D alone are used, two-graded display inblack-and-white is possible, while, when the points B, C, or the pointswhere electro-optical property (transmittance) rises in FIG. 2, areused, the display of intermediate gradation is possible.

As for the conventional electro-optical device utilizing TFTs, gradationdisplay was performed by varying the voltage applied to a gate or theTFT or that applied between source and drain thereof, and controllingthe voltage in an analogue mode.

Concerning the conventional method of gradation display in theelectro-optical device utilizing TFT, an explanation will be made: anN-channel thin film transistor used for the conventional electro-opticaldevice has the voltage-current characteristic as shown in FIG. 3, whichshows the voltage-current characteristic of the N-channel thin filmtransistor utilizing amorphous silicon, and of that utilizingpoly-silicon.

By controlling the voltage applied to a gate electrode of the thin filmtransistor having such characteristic in an analogue mode, drain currentcan be controlled and therefore strength of the electric field to beapplied to the liquid crystal can be varied, whereby gradation displayis possible.

In the case of an electro-optical device having picture elements of, forexample, 640×400 dots, however, it is difficult to manufacture all236,000 TFTs without variation in characteristics thereof. It is thoughtthat 15 gradation levels are limit of the number of gradation levels ofsuch electro-optical device having 640×400 picture elements in order toachieve productivity and yield required for practical process.

A gradation display may be performed by predetermining the value of gatevoltage, while controlling only the turning of ON/OFF by gate voltage,and by variably controlling source or drain voltage. In this case,however, about 16 gradation levels are considered to be a limit, basedon the fact that the characteristic are unstable. In an analogue mode ofthe gradation display control, clear display was difficult due tovariation in characteristics of TFT.

Another method of gradation display using multiple frames is suggested.As shown in the outline indicated in FIG. 11, when a gradation displayis to be performed using, for example 10 frames, by making two framesout of ten transparent, while the remainder of eight framesnontransparent, average 20% of transparency can be displayed at pictureelement A. A picture element B displays 70% of transparency on anaverage in the same manner, while a picture element C 50% oftransparency on an average.

When such a display is carried out, however, since the number of frameis practically reduced thereby, flickering and display failure weregenerated. To solve the problem, the increasing of frame frequency, orthe like, is suggested, whereas, the increase in power to be consumed inaccordance with the increase in driving frequency, as well as thedifficulty in the achievement of higher operation speed IC, indicated alimit of this method.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a method ofcompensating the variation in characteristics of TFT by inputting areference signal repeated in a certain cycle and having signal levelwhich varies during duration, of the reference signal, from a controllerside, in order to clarify the level of applied voltage, and bycontrolling the time of connecting the reference signal to the TFT bydigital value, and thereby controlling the voltage to be applied to theTFT. namely, to offer an electro-optical device by using complementarythin film transistors (C/TFTs) having a structure of modified transfergate (MTG) that performs digital gradation display.

The method is characterized in displaying gradation in anelectro-optical device using a display drive method that has a displaytiming in relation to a time F for writing one picture plane and a time(t) for writing in one picture plane, without changing the time F, byapplying a reference signal that has voltage variation in a cycle thatis equal to the time (t) to one of the signal lines that are used fordrive and selection of a picture element, as well as a selection signalat a certain timing within the time (t), to the other signal line,thereby determining the voltage to be applied to a liquid crystal, andthereby actually applying the voltage to the picture element.

In addition, the method is also characterized in high speed controlwithout being limited by several tens of MHz that was a limit of datatransfer speed for a conventional CMOS, since the timing is notdependent upon the transfer of the data, but is processed at a part forsignal process. with a high speed clock being added to a driver ICitself that is put on the electro-optical device.

FIG. 1 shows a concrete drive waveform for driving the electro-opticaldevice in accordance with the present invention. The electro-opticaldevice has a circuit configuration equivalent to a circuit diagramhaving a 2×2 matrix form shown in FIG. 4. Herein used is a half wave ofa sine wave, as the reference signal waveform of varied voltage in acertain period of time as described supra. Sine waves 303, 310 areapplied to V_(DD1) 303, V_(DD2) 304 that fall in a direction of ascanning line, while two-polarity (hereinafter referred to as bipolar)signals are applied to V_(GG1) 301, V_(GG2) 302 that fall in a directionof information line. Digital control is carried out by a timing ofapplying the bipolar signals.

Namely, the amount of charge to be accumulated at the point A as well aselectric potential at the point A are determined by changing the timingfor selecting the signal of varied voltage in a certain period of time,as shown in 309 and 310, and the size of the electric field to beapplied to the picture element as well as to the liquid crystal isdetermined by defining a certain value for the electric potential 313 ofa counter electrode.

The timing of applying the bipolar signal to gate signal lines such asV_(GG1), V_(GG2) is not determined by the transfer speed of theinformation signal, but is regulated by the reference clock input to thedriver IC that is directly connected to the electro-optical device inthe present invention. Namely, in the case of an electro-optical deviceof 640×400 dots, drive frequency is approximately 20 MHz based on thelimitation of CMOS, and, in order to calculate the number of gradationlevels by utilizing this value, the drive frequency is to be indicatedas a product of the number of scanning lines, the number of frames, thebipolar pulse, and the number of gradation levels, from which 20 MHz isdivided by (400×60×2), to obtain the number of gradation levels which is416, and it is needless to say that a display having 832 gradationlevels is possible by dividing the display screen into two.

The present invention is characterized in performing gradation displayin a digital method, instead of employing the conventional analoguemethod of gradation display. To obtain the effect, in the case of anelectro-optical device having picture elements of 640×400 dots, it isvery difficult to eliminate the variation in characteristics for all theTFTs of 256,000, at the time of manufacturing, and, practically, inconsideration of mass production and yield, 16 gradation display issupposed to be a limit, whereas, the method of compensating thevariation in characteristics of TFTs is employed in the presentinvention by inputting a reference signal from a controller side, inorder to clarify the level of applied voltage, and by controlling thetiming of connecting the reference signal to TFT by digital value, andthus controlling the voltage to be applied to TFT, which allows forclear digital gradation display.

Also, clear digital gradation display is possible without changing thenumber of frames for one picture plane, by defining two kinds of drivefrequency, whereby the generation of flickering concomitant with thedecrease in the number of frames can be prevented.

For example, when a gradation display is performed in a normal analoguemode for an electro-optical device, for which 256,000 pairs of TFTs of640×400 dots are formed in 300 nm square, a 16-gradation display is anupper limit due to the variation in TFT characteristics of approximately±10%. In the case of digital gradation display in accordance with thepresent invention, however, since the variation in characteristics ofTFT devices can be compensated, a 256-gradation display is possible, anda various and subtle color display of as many as 16,777,216 kinds ofcolors are possible thereby. When a software such as a television imageis to be projected on the screen, for example, the projection of a“rock” scene of the same color requires subtle difference in colors dueto the existence of slight recesses and the like thereon, and the16-gradation display is not suitable for the display as close to thenatural coloration ion as possible. However, the subtle variation intone can be displayed by the gradation display in accordance with thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe invention and together with the description, serve to explain theprinciple of the invention.

FIG. 1 shows an example of a drive waveform in accordance with thepresent invention.

FIG. 2 shows an electric photo-optical characteristic of theconventional electro-optical device.

FIG. 3 shows a current-voltage characteristic of TFT in the casepoly-silicon and amorphous silicon are adopted as materials used for theTFT.

FIG. 4 shows an example of a circuit of an active matrix electro-opticaldevice applicable to the present invention, subject to a part of 2×2matrix, structure.

FIG. 5 shows an example of a circuit of an active matrix electro-opticaldevice applicable to the present invention, subject to a part of 2×2matrix structure.

FIG. 6 corresponding to FIG. 5 shows the arrangement of an active matrixelectro-optical device applicable to the present invention.

FIGS. 7(A) to (I) corresponding to the first preferred embodiment, showschematic cross sectional views indicating the manufacturing process ofthe TFT applicable to the present invention.

FIG. 8 and FIG. 9 show schematic structure of the display deviceapplicable to the electro-optical device described in the presentinvention.

FIG. 10 shows a system structure of a drive circuit for anelectro-optical device applicable to the present invention.

FIG. 11 shows a concept of gradation display in accordance with theconventional method.

FIG. 12 shows the manufacturing process of forming a color filter on thesubstrate of the electro-optical device.

FIG. 13 corresponding to the third preferred embodiment, shows thearrangement of an active matrix electro-optical device applicable to thepresent invention.

FIGS. 14(A) to (G) corresponding to the second preferred embodiment,show schematic cross sectional views indicating the manufacturingprocess of the TFT applicable to the present invention.

FIG. 15 shows an example of a drive waveform in accordance with thepresent invention.

FIG. 16 shows an example of application I the electro-optical device inaccordance with the present invention, to a view finder.

FIG. 17 shows an example of the electro-optical device in accordancewith the present invention, of a front type projection television.

FIG. 18 shows a schematic structure of the electro-optical device inaccordance with the present invention.

FIG. 19 shows a system structure of a drive circuit of theelectro-optical device applicable to the present invention.

FIG. 20 shows an example of the application of the electro-opticaldevice in accordance with the present invention, to a personal computer.

FIG. 21 corresponding to the third preferred embodiment, shows thearrangement of the active matrix electro-optical device applicable tothe present invention.

FIGS. 22 (A) to (G) corresponding to the third preferred embodiment,show schematic cross sectional views indicating the manufacturingprocess of the TFT applicable to the present invention.

FIG. 23 is a circuit diagram showing an equivalent circuit in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred Embodiment 1

In this embodiment, a wall television is manufactured by using theliquid crystal display device having the circuit structure as shown inFIG. 5, which will be described infra. The manufacturing process of theTFT employed as an active device of the electro-optical device is shownin FIGS. 7 (A) through (I). Polycrystalline silicon that is subjected tolaser annealing process is used as a semiconductor material that formsthe TFT.

The arrangement of the electrode, etc. of the actual electro-opticaldevice corresponding to the circuit structure is shown in FIG. 6, whichshows only a part corresponding to 2×2 or less thereof forsimplification. The drive signal waveform that is actually usedtherefore is shown in FIG. 1, which also shows the signal waveform of2×2 matrix form for simplification.

Referring to FIG. 7, the manufacture of the liquid crystal panel used inaccordance with the preferred embodiment 1 will be described. Referringto FIG. 7(A), a silicon oxide film is manufactured to a thickness of1000-3000 angstroms as a blocking layer 51, by magnetron RF (highfrequency) sputtering, on the glass 50, which is not expensive, andwhich endure the heat treatment of not more than 700° C., e.g. ofapproximately 600° C., under the process condition of oxygen 100%atmosphere, deposition temperature of 15° C., output of 400 to 800 W,and the pressure of 0.5 Pa. The deposition rate was 30 to 100angstroms/minute when quartz or single crystalline silicon was used as atarget.

An intrinsic, or substantially intrinsic silicon film 52 wasmanufactured by plasma CVD thereupon. The deposition temperature rangedfrom 250° C. to 350° C., and it was 320° C. in the preferred embodiment1, using mono-silane (SiH₄) as a reactive gas, which can be replacedwith disilane (Si₂H₆) or trisilane (Si₃H₈). These were introduced in aPCVD device, and deposition was carried out by applying high frequencypower of 13.56 MHz under the pressure of 3 Pa. The suitable highfrequency power is 0.02 to 0.10 W/cm², while 0.055 W/cm² was adopted inthe preferred embodiment 1. The flow of mono-silane (SiH₄) was 20 SCCM,and the deposition rate at the time was approximately 120angstroms/minute. Boron can be added to the deposited film at aconcentration of 1×10¹⁵ to 1×10¹⁸ cm⁻³ using diborane during thedeposition, in order to control the threshold voltage (Vth) almost equalbetween PTFT and NTFT. Sputtering or low pressure CVD can be employedinstead of the plasma CVD for the deposition of the silicon layer thatwill be a channel region of TFT, and the methods will be described belowin simplified manner.

In the case of sputtering, the back pressure before sputtering was nomore than 1×10⁻⁵ Pa, and the sputtering was performed using a singlecrystalline silicon as a target, in the atmosphere in which 20-80 ? % ofhydrogen was added to argon: e.g. 20% of argon and 80% of hydrogen. Thedeposition temperature was 150° C., and the frequency was 13.56 MHz,while the sputtering output was 400-800 W, and the pressure was 0.5 Pa.In the case of low pressure CVD, deposition was carried out by supplyingdisilane (Si₂H₆) or trisilane(Si₃H₈) to a CVD device, at a temperatureof 450-550° C., 100 to 200° C. lower than that for crystallization, e.g.at 530° C. The pressure inside of the reactor was 30-300 Pa, while thedeposition rate was 50-250 angstroms/minute.

Oxygen in the film formed in these manner is preferably not more than5×10²¹ atoms·cm⁻³. It is preferred that the oxygen concentration be notmore than 7×10¹⁹ atoms·cm⁻³, desirably no more than 1×10¹⁹ atoms·cm⁻³,in order to promote crystallization, however, if it is too low, currentleakage under the OFF condition of TFT is increased due to theillumination of the back light of the electro-optical device, whereas,if it is too high, crystallisation becomes difficult, and thus laserannealing temperature must be increased or the laser annealing time mustbe prolonged. The concentration of hydrogen was 4×10²⁰ atoms·cm⁻³, andis one atom % compared to the silicon supposed to be 4×10²² atoms·cm⁻³.

The oxygen concentration can be not more than 7×10¹⁹ atoms·cm⁻³ ordesirably no more than 1×10¹⁹ atoms·cm⁻³, so as to promotecrystallization with regard to source or drain and oxygen can be addedonly to the channel forming region of the TFT that forms pixel, atconcentrations of 5×10²⁰ to 5×10²¹ atoms·cm⁻³ by ion implantation.

A silicon film an amorphous condition was formed at 500 to 5000angstroms in the above-mentioned manner, and at 1000 angstroms in thepreferred embodiment 1.

Referring to FIG. 7 (B), a photoresist pattern 53 is formed withopenings formed only on the source and drain regions in the photoresistpattern using a mask P1. A silicon film 54 was manufactured thereon,which is to be an n-type activation layer, by plasma CVD, at thedeposition temperature of 250° C. to 350° C., e.g. 320° C. in thepreferred embodiment 1, using mono-silane (SiH₄) and 3% concentration ofphosphine (PH₃) of mono-silane bass. These were introduced in the PCVDdevice at a pressure of 5 Pa, and the deposition was carried out byapplying a high frequency power of 13.56 MHz. The suitable highfrequency power is 0.05-0.20 W/cm², and it was 0.120 W/cm² in thepreferred embodiment 1.

The electric conductivity of the n-type silicon layer formed in theabove-mentioned manner was approximately 2×10⁻¹ [(Ω·cm)⁻¹], while thefilm thickness was 50 angstroms. The resist 53 was then removed bylift-off method, so as to form source, drain regions 55, 58.

A p-type silicon semiconductor layer was formed using the same process.Mono-silane (SiH₄) and 5% concentration of diborane (B₂H₆) ofmono-silane base were used as the introduction gas. These wereintroduced in the PCVD device at a pressure of 4 Pa, and deposition wascarried out by applying a high frequency power of 13.56 MHz. Thesuitable high frequency power is 0.05 to 0.20 W/cm², and 0.120 W/cm² wasadopted in the preferred embodiment 1. The electric conductivity of thep-type silicon layer formed in this manner was approximately 5×10⁻²[(Ω·cm)⁻¹], while the film thickness was 50 angstroms. Source, drainregions 59, 60, were formed by using the lift-off method in the samemanner as the n-type region. The silicon film 52 was then etched off,using a mask P3, and an island region 33 for N-channel thin filmtransistor as well as an island region 64 for P channel thin filmtransistor were formed.

The source, drain and channel regions were laser-annealed using XeClexcimer laser, while a laser doping was carried out to the activationlayer. As for the laser energy at the time, a threshold energy was 130mJ/cm², whereas 220 mJ/cm² was required so as to melt the entire filmthickness. When the energy of no less than 220 mJ/cm² is irradiated fromthe start, hydrogen included in the film is abruptly ejected, wherebythe film is damaged. For that reason, melting has to be carried outafter the hydrogen is primarily purged at a low energy. In the preferredembodiment 1. after the hydrogen was at first purged at 150 mJ/cm²,crystallization was carried out at 230 mJ/cm².

By the annealing, the silicon film is transformed from an amorphousstructure to the state of higher order, with a part thereof beingcrystallized. In particular, a relatively higher order region of thesilicon coated film tends to be crystallized into a crystalline regionby the annealing. However, silicon atoms are pulled with each othersince bonds are formed between such regions by silicon atoms existingtherebetween. Laser Raman Spectroscopy results show a peak shifted tothe frequency lower than the single crystalline silicon peak of 522cm⁻¹. The apparent grain diameter was calculated 50 to 500 Å, based on ahalf band width, however, in fact, the film comprises a lot of highcrystalline regions which constitute a cluster structure, and clustersare anchored to each other in the film by bonds between silicon atoms.

As a result, it can be said that substantially no grain boundary(hereinafter referred to as GB) exists in the film. Since carriers caneasily move between the respective clusters, through the anchoredportions, a carrier mobility higher than that of a poly-crystallinesilicon in which a GB obviously exists, is achieved. Namely, Hallmobility (μh) of 10-200 cm²/Vsec, electron mobility (μh) of 15-300cm²/VSec can be obtained.

A silicon oxide film was formed as a gate insulating film thereon in thethickness ranging from 500 to 2000 Å, e.g., at 1000 Å, under the samecondition as that for the manufacturing of the silicon oxide film as ablocking layer. At the time of forming the film, a small amount offluorine may be added thereto, so as to stabilize sodium ion.

Further, on the upper surface thereof, a silicon film doped withphosphorus at 1 to 5×10²¹ atoms·cm⁻³, or a multi-layered film comprisingthis silicon film and molybdenum (Mo), tungsten (W), MoSi₂ or WSi₂ filmformed thereupon, was formed, which was then subjected to a patterningprocess using a fourth photomask P4, and the structure shown in FIG.7(E) was thereby obtained. A gate electrode 56 for NTFT, as well as agate electrode 67 for PTFT ware formed: e.g. a channel length of 7 μm;and as a gate electrode P-doped Si of 0.2 μm on which molybdenum wasformed at 0.3 μm.

In the case aluminum (Al) is used as a gate electrode material, afterpatterning the gate electrode material by a fourth photomask 69, anodicoxidation can be applied to the surface thereof. In this case, aself-aligning process can be employed, whereby the contact hole of asource and drain can be formed closer to the gate, and the TFTcharacteristic can be further improved thereby, due to the improvedmobility as well as the reduction in threshold voltage.

In this way, C/TFT can be manufactured without elevating the temperaturenot less than 400° C., in every process. Therefore, it is not necessaryto use an expensive material such as quartz for the substrate, and itcan be said that this is a most suitable process for manufacturing thewide-screen liquid crystal display device in accordance with the presentinvention.

Referring to FIG. 7(F), an inter-layer insulating material 68 wassputtered, so as to form a silicon oxide film, in the manner describedsupra. The silicon oxide film can be formed by LPCVD, photo-CVD, or byatmospheric pressure CVD, at a thickness of, for example, 0.2 to 0.6 μm,and thereafter, an opening 79 for electrode was formed using a fifthphotomask P6. In addition, after aluminum was formed by sputtering at athickness of 0.3 μm thereupon, while a lead 74 as well as contacts 73,75 were manufactured using a sixth photomask P6, an organic resin 77 forflattening, for example, a translucent polyimide resin was applied toand farmed on the surface, and an opening for electrode was formed againby a seventh photomask P7. An ITO (indium tin oxide) was formed en thesurface thereof, at a thickness of 0.1 μm by sputtering, and a pictureelement electrode 71 was formed using an eighth photomask P8. The ITOwas formed at a temperature ranging from room temperature to 150° C.,and was subjected to annealing process at 200-400° C. in oxygen oratmosphere.

The electric characteristics of P-TFT thus obtained were: mobility of 40(cm²/Vsec), Vth of −5.9 (V), while those of NTFT were: mobility of 80(cm²/Vsec), and Vth of 5.0 (V).

In this manner, one substrate for the electro-optical devicemanufactured in accordance with the present invention, was obtained.

The wirings of the electrode, etc., of the liquid crystal display deviceare shown in FIG. 6. An N-channel thin film transistor and a P-channelthin film transistor are provided on the intersection of a first signalline 3 and a second signal line 4, whereby the device has a matrixstructure with the use of a modified TG type C/TFT. TFT 13 is connectedto the second signal line 4 through a contact of an input terminal of adrain 10, while a gate 9 is connected to the first signal line 3. Theoutput terminal of a source 12 is connected to an electrode 17 of thepicture element through a contact.

On the other hand, regarding PTFT 22, the input terminal of a drain 20is connected to the second signal line 4 through a contact, while a gate21 is connected to the signal line 3, and the output terminal of asource 18, to the picture element electrode 17 through a contact, in thesame manner as NTFT. By repeating such a structure horizontally andvertically, the liquid crystal display device having picture elements asmany as 540×480, 1280×980, or 1920×400 in this embodiment, can beobtained.

In this way, a first substrate of a pair of substrates was obtained.

The manufacturing method of the other, or a second substrate is shown inFIG. 12. A striped color filter is provided on the substratecorresponding to each picture element. The polyimide resin mixed withblack pigment was formed on a glass substrate at a thickness of 1 μm, byspin coating, and a black stripe 81 was formed using a ninth photomaskP9. Then, the polyimide resin mixed with a red pigment was formed at 1μm by spin-coating, and a red filter 83 was formed using a tenthphotomask P10. A green filter 85 and a blue filter 86 were formed is thesame manner, using masks P11, P12. Each filter was baked in nitrogen forsixty minutes, at a temperature of 350° C. during the manufacturethereof. A leveling layer 89 was then manufactured using transparentpolyimide, again by spin coating.

An ITO (indium tin oxide) was then formed on the entire filter at athickness of 0.1 μm by sputtering, and a common electrode 80 was formedusing a fifth photomask P13. The ITO was formed at a temperature rangingfrom room temperature to 150° C., and was subjected to the annealingprocess at 200 to 300° C. in oxygen or atmosphere, so as to obtain acolor filter layer and the electrode 90 on the second substrate.

A polyimide precursor was printed on the substrate by an offset method,was baked in a non-oxidating atmosphere, e.g. in nitrogen, for an hour,at a temperature of 330° C., and was subjected to a known rubbingmethod, whereby the surface condition of the polyimide was changed, anda means to allow for a liquid crystal molecule to be oriented in acertain direction at least in the initial stage was provided.

The nematic liquid crystal composition was sandwiched by the first andthe second substrates as described above. The periphery of the first andthe second substrates is fixed with an epoxy adhesive. A TAB shapeddriving IC and a PCB comprising common signal and electric potentialwirings are connected to leads provided on the substrate, and apolarizing plate was attached to the outside thereof, so as to obtain atransmission type electro-optical device.

A schematic diagram of the electro-optical device in accordance withthis embodiment is shown in FIGS. 8 and 9. The liquid crystal panel 220manufactured in the processes described above was installed by combiningit with a rear part lighting device 221 comprising three pieces of coldcathode tubes arranged thereon, and was then connected to a tuner 223for receiving television radio wave, so as to complete theelectro-optical device. Since the device has a flat shape compared withthe conventional one of CRT type, it can be installed on the wall, andthe like.

Referring to FIG. 10, the driving peripheral circuit of theelectro-optical device in accordance with the present invention will beexplained:

A driving circuit 352 is connected to the wirings 350, 351 on the sideof an information signal, connected to the matrix circuit of theelectro-optical device. The driving circuit 352 comprises two parts whendivided by a driving frequency system, i.e. one is a data latch circuitsystem 353, which is the same as in the conventionally known drivingmethod, and which primarily comprises a basic dock CLK signal circuit355 for transferring the signals of a data signal circuit 356 in order,performing one bit to twelve bits parallel processing. The other is apart in accordance with the present invention, and comprises a clock 357corresponding to the degree of division necessary for gradation display,a flip flop circuit 358, and a counter 360. The counter 360 forms abipolar pulse generation timing corresponding to the gradation displaydata sent from the data latch system 353. Further, the gradation displaydata can be controlled in finer way, when a ROM table for converting Δtinto sinθ is used between the exit of the latch circuit and a data line361.

The present invention is characterized in that the clear digitalgradation display is possible without changing the number of frames forre-writing the screen, by taking two kinds of driving frequencies. Thegeneration of flickering and the like caused by the decrease in thenumber of frames can be prevented thereby.

On the other hand, a driving circuit 364 connected to signal lines 363,362 on a scanning side controls the sine wave transmitted from a sinewave oscillating circuit 365 by a flip flop circuit 356 of a clock CLK,367, and the select signal is applied to the signal lines 363, 362.

By digitally controlling the timing for cutting the sine wave signal onthe scanning side by the bipolar pulse on the information side,gradation display is possible.

When an analogue gradation display is carried out in a normal mode forthe electro-optical device comprising, for example, 788,000 pairs ofTFTs of 1920×400 dots formed into a 300 mm square, the variation incharacteristics of the TFTs becomes ±10% as a whole, and thus agradation display having 16 gradation levels is an upper limit, whereas,when a digital gradation display is carried out in accordance with thepresent invention, it is hardly affected by the variation incharacteristics of TFTs, and a gradation display having 64 gradationlevels is thus possible for the electro-optical device of the same size,while various and subtle expression of 262,144 kinds of colors isachieved in color-display.

Preferred Embodiment 2

The formation of a view finder for a video camera utilizing anelectro-optical device haying a diagonal of one inch in accordance withthis second preferred embodiment 2 will be described below.

In this embodiment, the number of picture elements was 357×125, and thedevice was formed using a high mobility TFT obtained by a lowtemperature process, so as to form the view finder. The arrangement ofthe active device on the substrate of the liquid crystal display deviceused in this embodiment is shown in FIG. 13, and the manufacturingprocess of the TFT part is shown in FIG. 14 in such a way that eachcorresponds to A-A′ cross section and B-B′ cross section shown in FIG.13. Referring to FIG. 14(A), a silicon oxide film is manufactured at athickness of 1000 to 3000 Å as a blocking layer 51 by magnetron RF (highfrequency) sputtering, on the inexpensive glass substrate 50 that bearsheat treatment of no more than 700° C., e.g. approximately 800° C. Theconditions for the process are: 100% oxygen atmosphere, formationtemperature of 15° C., output of 400 to 800 W, and pressure was 0.5 Pa.The formation rate using quartz or single crystalline silicon as atarget was 30 to 100 Å/min.

A silicon film was then formed thereon by LPCVD (low pressure chemicalvapor deposition), sputtering, or by plasma CVD. When the low pressurechemical vapor deposition was employed, film formation was carried outby supplying disilane (Si₂H₆) or trisilane (Si₃H₈) to a CVD device, at atemperature of 450 to 550° C., 100 to 200° C. lower than the temperaturefor crystallization, e.g. at 530° C. The pressure in a reactor was 30 to300 Pa, while the film formation rate was 50 to 250 Å/min. Boron may beadded to the film using diborane at a concentration of 1×10¹⁵ to 1×10¹⁸atoms·cm⁻³, during the manufacture thereof, in order to control thethreshold voltages (Vth) for PTFT and NTFT almost of the same.

In the case of the silicon film formation by sputtering, the backpressure before sputtering was not more than 1×10⁻⁵ Pa, and theformation was carried out in the atmosphere comprising 20 to 80% ofhydrogen mixed with argon; e.g. argon 20% and hydrogen 80%, using singlecrystalline silicon as a target. The formation temperature was 150° C.,and the frequency of high frequency power applied thereto was 13.56 MHz,sputtering output was 400 to 800 W, and the pressure was 0.5 Pa.

Silicon film formation by plasma CVD was carried out at a temperatureof, for example, 300° C., using mono-silane(SiH₄) or disilane(Si₂H₆),which were introduced in a PCVD device, and high frequency power of13.56 MHz was applied thereto, so as to carry out film formation.

Oxygen in the film formed by these methods is preferably not more than5×10²¹ cm⁻³. If the oxygen concentration is too high, crystallization ishard to occur, and the temperature of thermal annealing has to beelevated, or else, the time of thermal annealing has to be longer. Ifthe concentration is too low, the leakage current in an OFF state isincreased due to the back light. For that reason, the concentrationrange was defined from 4×10¹⁹ to 4×10²¹ atoms·cm⁻³. Hydrogenconcentration was 4×10²⁰ atoms·cm⁻³, or one atoms % compared to thesilicon of 4×10²² atoms·cm⁻³.

After a silicon film is amorphous state was manufactured at a thicknessof 500 to 5000 Å, e.g. at 1500 Å, in the manner described above, middletemperature heat treatment was carried out in a non-oxidating atmosphereat a temperature of 450 to 700° C., for 12 to 70 hours, for example, thefilm was maintained at a temperature of 800° C. in a hydrogenatmosphere. Since the silicon oxide film is amorphous structure isformed on the substrate surface under the silicon film, a specificnucleus does not exist due to the heat treatment, and the entire body isuniformly thermal-annealed. Namely, amorphous structure is retainedduring the manufacture of the film, and hydrogen is simply mixedtherein.

The silicon film was transformed from the amorphous structure into thestate of higher order, through the annealing, with a part thereof beingcrystallized. In particular, a relatively higher order region of thesilicon coated film tends to be crystallized into a crystalline regionby the annealing. However, silicon atom are pulled with each other sincebonds are formed between such regions by silicon atoms existingtherebetween. Laser Raman Spectroscopy results show a peak shifted tothe frequency lower than the single crystal silicon peak of 522 cm⁻¹.The apparent grain diameter thereof is calculated 50-500 Å, based on ahalf band width, seemingly like the case of a micro-crystal, however,actually, a film in semi-amorphous structure was formed includingtherein high crystalline regions constituting a cluster structure,clusters being anchored to each other by bonds between silicon atoms.

As a result, it can be said that substantially no GB exits in the film.Since carriers can easily move between each cluster through the anchoredportions, mobility higher than that of polycrystalline silicon in whichGB obviously exists, is obtained. Namely, Hall mobility (μh) of 10 to200 cm²/Vsec, electron mobility (μe) of 15 to 300 cm²/Vsec can beobtained.

When polycrystallization of the film is carried out by high temperatureannealing process at 900-1200° C., instead of the above-mentioned middletemperature annealing process, segregation of impurities in the filmoccurs due to the solid growth from nucleus, whereby impurities such asoxygen, carbon, nitrogen are increased in the GB, and, although themobility in crystal is higher, the movement of carriers is hindered by abarrier formed by the GB. Consequently, the mobility no less than 10cm²/Vsec cannot be achieved in practice. From that reason, the siliconsemiconductor having semi-amorphous or semi-crystalline structure isused in this embodiment.

Referring to FIG. 14(A), a silicon film is photo-etched by a firstphotomask P14, and a region 13 (channel width of 20 μm for NTFT wasmanufactured on the side of the A-A′ cross section shown in the figure,while a region 22 for PTFT on the side of B-B′ cross section.

A silicon oxide film was formed thereon at a thickness of 500 to 2000 Å,e.g. at 1000 Å, as a gate insulating film. The manufacture thereof wascarried out under the same conditions for those applied for themanufacture of the silicon oxide film as a blocking layer. A smallamount of fluorine may be added during the manufacture thereof, so as tostabilize sodium ion.

On the upper surface thereof, a silicon film doped with phosphorus at 1to 5×10²¹ atoms·cm⁻³, or a multi-layered film comprising this siliconfilm and molybdenum (Mo), tungsten (W), MoSi₂ or WSi₂ film formedthereupon, was formed, which was then subjected to a patterning processusing a second photomask P15, and the structure shown in FIG. 14(B) wasthereby obtained. A gate electrode 9 for NTFT, as well as a gateelectrode 21 for PTFT were formed. In this embodiment, as a gateelectrode P-doped Si of 0.2 μm and molybdenum of 0.3 μm thereon wereformed and channel length of the NTFT was 10 μm and channel length ofthe PTFT was 7 μm. Referring to FIG. 14(C), boron was ion-doped at adose of 1 to 5×10¹⁵ cm⁻², to a source 18 and a drain 20 for PTFT.Referring to FIG. 14(D), then, a photoresist 61 was formed using aphotomask P16. Phosphorus was ion-doped at a dose of 1 to 5×10¹⁵ cm⁻²,as a source 10 and a drain 12 for NTFT.

In the case aluminum (Al) is used as a gate electrode material, afterpatterning the gate electrode material by a second photomask P16, anodicoxidation can be applied to the surface thereof. In this case, aself-aligning process can be employed, whereby the contact hole of asource and drain can be formed closer to the gate, and the TFTcharacteristic can be further improved thereby, due to the improvedmobility as well as the reduction in threshold voltage.

Thermal annealing process was again carried out at 600° C., for 10 to 50hours. By activating impurities, a source 10, a drain 12 of NTFT and asource 18, a drain 20 of PTFT ware manufactured as P⁺ type and N⁺ type.Channel forming regions 19, 11 are formed as semi-amorphoussemiconductors, under gate electrodes 21, 9.

In this way, C/TFT can he manufactured without elevating the temperaturenot less than 700° C. in every process.

Therefore, it is not necessary to use an expensive material such asquartz for the substrate, and this is a most suitable process formanufacturing the wide-screen liquid crystal display device inaccordance with the present invention.

The thermal annealing process was carried out twice in this embodiment,as shown in FIG. 14 (A), (D). However, the annealing process shown inFIG. 14(A) may be omitted dependent upon the desired characteristics,and the manufacturing time can be shortened by replacing these twoannealing processes with only one annealing process shown in FIG. 14(D).

Referring to FIG. 14(E), a silicon oxide film 65 was formed as aninterlayer insulating film by sputtering as described supra. The siliconoxide film can be formed by LPCVD, photo-CVD, or by atmospheric pressureCVD. The thickness thereof was, for example, 0.2 to 0.6 μm. Thereafter,an opening 56 for electrode was formed using a photomask P17. Aluminumwas then sputtered on the surface of the entire structure, as shown inFIG. 14(F), and after a lead 71 as well as a contact 72 was manufacturedusing a photomask P18, an organic resin 69 for flattening, for example,a translucent polyimide resin was applied to and formed on the surfacethereof, and an opening for electrode was formed again by a photomaskP19.

An ITO (indium tin oxide) was formed by sputtering, so as to form twoTFTs in a complementary structure, and to connect the output terminalthereof to one picture element electrode of the liquid crystal device,as a transparent electrode. It was then etched using a photomask P20,and an electrode 17 was formed thereby. The ITO was formed at atemperature ranging from room temperature to 150° C. and then annealedat 200 to 400° C. in oxygen or atmosphere. The electric characteristicsof the TFT thereby obtained were: mobility of 20 (cm²/Vsec), Vth of −5.9(V) for PTFT: and mobility of 40 (cm²/Vsec), and Vth of 5.0 (V) forNTFT.

In this manner, one substrate for the liquid crystal device wasmanufactured. The arrangement of the electrode, etc., of the liquidcrystal display device is shown in FIG. 13. NTFT 13 and PTFT 22 wereprovided on the intersection of a first signal line 3 and a secondsignal line 4, whereby the device has a matrix form using C/TFT. NTFT 13is connected to the second signal line 4 through the contact of theinput terminal of a drain 10, while a gate 9 is connected to the signalline 3 forming a multi-layered wiring. The output terminal of a source12 is connected to an electrode 17 of the picture element through acontact.

On the other hand, regarding PTFT 22, the input terminal of a drain 20is connected to the second signal line 4 through a contact, while a gate21 is connected to the signal line 3, and thB output terminal of asource 16, to the picture element electrode 17 through a contact, in thesame manner as NTFT. This embodiment is formed by repeating such astructure horizontally and vertically.

An ITO (indium tin oxide) was then formed by sputtering on the soda-limeglass plate on which a silicon oxide film was formed by sputtering at athickness of 2000 Å. The ITO was formed at a temperature ranging fromroom temperature to 150° C., and was subjected to the annealing processat 200 to 300° C. in oxygen or atmosphere. A color filter layer was thenformed thereon in the same manner as described in the PreferredEmbodiment 1 to obtain a second substrate.

A polyimide precursor was then printed on the substrates by an offsetmethod, and was baked in a non-oxidation atmosphere, e.g. in nitrogen,for an hour, at a temperature of 350° C. It was then subjected to aknown rubbing method, so as to change the surface condition of thepolyimide, and a means to allow for a liquid crystal molecule to beoriented in a certain direction at least in the initial stage wasprovided.

The nematic liquid crystal composition was sandwiched by the first andthe second substrates as described above, after fixing the periphery ofthe first and second substrates by an epoxy adhesive. Since the pitch ofthe leads on the substrate was as fine as 46 μm, connection was made bya COG method, in this embodiment, a gold bump provided on an IC chip wasconnected, by an epoxy silver palladium, and the IC chip and thesubstrata were buried and fixed by epoxy metamorphic acrylic resin forsolidification and the sealing of these. A polarizing plate was thenattached to the outside thereof, and a transmission type liquid crystaldisplay device was obtained.

The driving waveform, used in this embodiment is shown in FIG. 15. Inthis embodiment, a ramp wave is used as shown in FIG. 15. Formation of aramp wave is easy and it is easy to convert original gradation data intoΔt in the ramp wave. FIG. 16 shows a view finder in accordance with thisembodiment and a video camera utilizing the view finder. The videocamera comprises the electro-optical device 370 manufactured in themanner described supra and a cold cathode tube 371 having flat emission.

When an analogue gradation display is carried out in a normal mode forthe electro-optical device comprising, for example, 49,152 pairs of TFTsof 384×128 dots formed into a 50 mm square (which is obtained bydividing a substrate of 300 nm square into 36 pieces), the variation inTFTs characteristics is ±10% as a whole, and a gradation display havingis gradation levels is thus an upper limit, whereas, when a digitalgradation display is carried out in accordance with the presentinvention, it is hardly affected by the variation in TFTscharacteristics, and a gradation display having 128 gradation levels isthereby possible, while various and subtle expression of 2,097,152 kindsof colors is achieved in a color display mode.

Preferred Embodiment 3

In this embodiment, a projection type image display device as shown inFIG. 17 will be explained.

In this embodiment, the image projecting part for the projection typeimage display device was assembled by three electro-optical devices 201.Each of devices 201 has a 640×480 dots, and 307,200 picture elementswere manufactured in a four-inch diagonal: the size per one pictureelement was 127 μm square.

As the structure of the projection type image display device, theelectro-optical devices 201 were installed by dividing into threeelementary colors of red, green, and blue: it comprises a red filter202, a green filter 203, a blue filter 204, a reflecting plate 205,prism mirrors 206, 207, a metal halide light source 208 of 150 W, and anoptical system 209 for focusing.

The substrate of the electro-optical device in accordance with thisembodiment was the same as that manufactured in the manner described inthe Preferred Embodiment 2, and has a matrix circuit of C/MOS structure.The liquid crystal material used in this embodiment was of dispersiontype or polymer dispersion type.

A schematic diagram is shown In FIG. 18. A mixture comprising a fumaricacid polymer resin and a nematic liquid crystal at a ratio of 65:35mixed in a common solvent of xylene was formed on the substrate 210 at athickness of 10 μm by a die-cast method. Then, the solvent was removedin nitrogen atmosphere at a temperature of 120° C., for 180 minutes, anda liquid crystal dispersion layer 211 was formed thereby. Conduct timecan be shortened by reducing the pressure slightly lower thanatmosphere.

An ITO (indium tin oxide film) was formed by sputtering, so as to obtaina counter electrode 212. The ITO was formed at a temperature rangingfrom room temperature to 150° C. A translucent silicon resin was appliedthereon at a thickness of 30 μm, by printing, and was baked for thirtyminutes at 100° C., so as to obtain the electro-optical device.

The driving IC used in this embodiment is shown in FIG. 19, Thestructure of the information electrode side is the same as described inthe Preferred Embodiment 1. In a driving circuit 400 connected to thewirings 405, 407 on scanning side, the ramp wave transmitted from a rampwave oscillating circuit 405 is controlled by flip flop circuits 403,404 of a clock CLK 406, and a select signal is added thereto.

A gradation display is possible by digitally controlling the timing forcutting the ramp wave on the side of a scanning line by a bipolar pulseon the side of an information line.

For example, when a gradation display is performed in a normal analoguemode for the electro-optical device comprising 307,200 pairs of TFTs of640×480 dots formed in 300 mm square, 16 gradation levels are an upperlimit due to the variation in TFT characteristics of approximately ±10%.In the case of digital gradation display in accordance with the presentinvention, however, since it is hardly affected by the variation incharacteristics of TFT devices, a gradation display having 258 gradationlevels is possible, while a various and subtle display of as many as16,777,216 kinds of colors is possible.

The electro-optical device can be applied not only to a front typeprojection television as illustrated in FIG. 17, but also to a rear typeprojection television.

Preferred Embodiment 4

In this embodiment, an electro-optical device for portable computer wasmanufactured using a reflection type liquid crystal dispersion displaydevice as shown in FIG. 20, and the explanation thereof will be hereinmade:

The first substrate used in this embodiment was the same as thatmanufactured in the process in accordance with the PreferredEmbodiment 1. A nematic liquid crystal and a fumaric acid polymer resinmixed therein 15% of a black pigment at a ratio of 35:85 were dissolvedin a common solvent of xylene. The solution was applied on the substrate210, at a thickness of 10 μm, by a die-cast method. The solvent was thenremoved in nitrogen atmosphere at 120° C., for 180 minutes, and a liquidcrystal dispersion layer 211 was formed thereby.

As the black pigment is used therein, black color appears at the time oflight scattering or at the time of application of no electric field,while white color is displayed in a transmission state or at the time ofapplication of electric field, whereby a flat display that was difficultfor a dispersion type liquid crystal display is possible like that ofthe letter written on a sheet of paper.

An ITO (indium tin oxide film) was then formed by sputtering, so as toobtain a counter electrode 212. The ITO was formed at a temperatureranging from room temperature to 150° C. A white-colored silicon resinwas applied thereon at a thickness of 55 μm, by printing, and was bakedfor ninety minutes at a temperature of 100° C., so as to obtain theelectro-optical device.

As a modification of this embodiment, no black pigment was contained inthe liquid crystal dispersion layer 211. In this case, the rear surfacehas to be made black. In this case, white color appears at the time oflight scattering, while black color is displayed in a transmissionstate. A flat display was possible like that of the letter written on asheet of paper.

Preferred Embodiment 5

In this embodiment, an electro-optical device provided with modifiedtransfer gate TFTs in complementary structure for one picture elementwas manufactured by anodic oxidation technique, as shown in FIG. 21. Themanufacture of the TFTs in accordance with this embodiment is basicallythe same as that in accordance with the first preferred embodiment, andits processes proceed almost in the same manner as shown in FIG. 7,however, since the anodic oxidation technique was employed as mentionedabove, metallic material was used as a gate electrode material, so as toutilize the anodic oxidation film thereof as a part of an insulatingfilm, whereby manufacturing process was slightly changed.

Referring to FIG. 21, PTFT 95 and NTFT 96 are connected to a common gatewiring 107 at gate terminals thereof, and one of source and drainregions of the PTFT and one of source and drain regions of the NTFT areconnected together and connected to the other signal line 102. The otherone of the source and drain regions of the NTFT are connected to acommon picture element electrode 108.

Referring to FIGS. 22(A) to 22(G), a silicon oxide film as a blockinglayer 99 was manufactured on the glass substrate 98, at a thickness of1000 to 3000 Å, by magnetron RF (high frequency) sputtering. Theconditions for the process are: 100% oxygen atmosphere, film formationtemperature of 15° C., output of 400 to 800 W, and the pressure of 0.5Pa. The film formation rate was 30 to 100 Å/min. using quartz or singlecrystalline silicon as a target.

A silicon film 97 was formed thereon by LPCVD (low pressure chemicalvapor deposition), sputtering, or by plasma CVD.

Referring to FIG. 22(A), the silicon film was photo-etched using a firstphotomask P21, and a region for PTFT was manufactured on the left handside of the figure, as well as that for NTFT on the right hand sidethereof.

A silicon oxide film as a gate insulating film 103 was formed thereon ata thickness of 500 to 2000 Å, e.g. at 700 Å. The manufacture thereof wascarried out under the same conditions employed for the silicon oxidefilm 99 as a blocking layer.

The alloy of aluminum and silicon was formed thereon as a material for agate electrode 107, at a thickness of 3000 Å to 1.5 μm, e.g. at 1 μm, bya known sputtering method.

As the material for the gate electrode beside aluminum silicide,molybdenum (Mo), tungsten (W), titan (Ti). tantalum (Ta). chromium (Cr),or an alloy of these material or an alloy of silicon and these material,or a multi-layered film comprising a silicon layer and a layer of thesemetal can be used.

Further, a silicon oxide film was formed as an insulating film 106, at athickness of 3000 Å to 1 μm, or at 3000 Å in this embodiment, bysputtering, on the gate electrode material. Then, the insulating film106 and the gate electrode 107 were subjected to a patterning processusing a second photomask P22, and the gate electrode 107 as well as theinsulating film 106 were formed as shown in FIG. 22(B).

The substrate was then dipped in an AGW electrolytic solution in whichpropylene glycol was added to a 3% of tartaric acid solution at a ratioof 9:1, while the gate electrode of aluminum silicide was connected tothe anode of a power source, and dc power was applied thereto withplatinum used as a cathode, Each of the gate electrodes was connected tocorresponding gate wiring and all the gate wirings are connected by aterminal in the vicinity of an end part of the substrate and an anodicoxidation film 100 was formed in the vicinity of the side surface of thegate electrode by anodic oxidation, as shown in FIG. 22(C).

As the solution used for the anodic oxidation, typically, a strong acidsolution such as sulfuric acid, nitric acid, phosphoric acid, or a mixedacid such as tartaric acid or citric acid mixed with ethylene glycol orpropylene glycol, can be used. Salt or alkali solution may be mixedthereto, in order to adjust pH or the solution, when required.

The anodic oxidation was carried out as follows: after current was runat the current density of 2.5 mA/cm² in a constant current mode, forthirty minutes, then five minutes of process in a constant voltage modefollowed, so as to form an aluminum oxide film of 2500 Å in the vicinityof the side surface of the gate electrode. When the insulatingcharacteristic of the aluminum oxide was measured using a samplemanufactured under the same conditions employed for this oxidationprocess, resistivity was 10⁹ ohm·meter, and dielectric strength was2×10⁶V/cm.

The observation of the surface of the sample by a scanning electronmicroscope revealed unevenness on the surface in an approximately 8000magnifying power mode, however, no fine hole was observed, which meansthe evidence of a good insulating film.

After an insulating film 103 on the semiconductor was removed by etchingas shown in FIG. 22(D), boron was ion-implanted at a dose of 1 to 5×10¹⁵cm⁻² as an impurity for PTFT, on the entire surface of the substrate.The doping was carried out at a concentration of approximately 10¹⁹atoms·cm⁻², so as to form a source, drain region of PTFT. In thisembodiment, ion doping was carried out after the insulating film on thesurface was removed, however, if the conditions for ion-implantation arechanged, doping is possible through the insulating film 103 on thesemiconductor film.

A photoresist 110 was formed using a third photomask P23 as shown inFIG. 22(E), and after a PTFT region was covered therewith, phosphoruswas ion-implanted at a dose of 1 to 5×10¹⁵ cm⁻², to the source and drainregion for NTFT, so as to obtain a dope concentration of approximately10²⁰ atoms·cm⁻³. In the ion doping process as described above, theion-implanting direction was set oblique to the substrate, in order toallow for the impurity to penetrate into a portion of the semiconductorunder the anodic oxidation film in the vicinity of the gate electrode,so as to make the end of the source and drain regions 104, 105 almostidentical with the end of the gate electrode. Sufficient insulatingfunction is thereby expected for an anodic oxidation film 100 to anelectrode wiring to be formed in a following process, and it is thus notnecessary to form another insulating film.

Activation process was carried out by irradiating a laser beam to thesource and drain regions. Since the activation process was carried outinstantaneously, at the time, it is not necessary to consider thediffusion of the metallic material used for the gate electrode, and TFTof high reliability was manufactured.

Aluminum was formed on the entire surface thereof by sputtering, andafter an electrode lead 102 was obtained by patterning using a fourthmask P24, the semiconductor which does not overlap with an electrode102, an insulating film 106 on the gate electrode 107, and the anodicoxidation film 100 in the vicinity of the side surface of the gateelectrode 107 was etched off, and a complete device separation wascarried out so as to complete TFT. In this manufacturing method,complementary TFTs were manufactured using four pieces of masks, whichis shown in FIG. 22(F).

Referring to FIG. 22(G), to achieve complementary TFTs, and to connectthe output terminal thereof to one picture element electrode of theliquid crystal device as a transparent electrode, an ITO (indium tinoxide film) was formed by sputtering, and was etched using a fifthphotomask {circle around (5)} so as to form a picture element electrode108.

In this way, modified transfer gate TFTs having arrangement andstructure as shown in FIG. 21(A), (B), (C), were completed. FIG. 21(B)is a cross sectional view corresponding to a F-F′ cross section shown inFIG. 21(A), while FIG. 21(C) is a cross sectional view corresponding toan E-E′ cross section shown in FIG. 21(A). As clearly shown in FIG.21(B), (C), the interlayar insulating film 10S invariably exists on thegate electrode 107, and it works sufficiently as an interlayarinsulating means at an intersection of the lead part of a gate wiring107 and that of a source or drain wiring 102, whereby the generation ofwiring capacity at the intersection was able to be suppressed.

In this embodiment, complementary TFTs having structure in which thecapacity in the vicinity of wirings is less, and the fear ofshort-circuit in the vicinity of the gate insulating film is less couldbe formed using masks fewer than those used in the first preferredembodiment, without employing a higher-grade process technique such asan anisotropic etching to provide an active element substrate.

The substrate formed in the manner described above was used as a firstsubstrate and a second substrate (counter substrate) was formed byforming a counter electrode on a substrate and further forming anorientation control film thereon. The first and second substrates werejoined with each other and an STN type liquid crystal was injectedbetween the first and second substrate by a known technique. An activematrix type STN liquid crystal electro-optical device was thencompleted.

The applications to the electro-optical device were described in theabove examples, however, the present invention is not limited theretoand the application to other devices or to a three-dimensionalintegrated circuit device, and so on, is also possible.

The manufacture of TFT device was possible in this embodiment, usingmasks much fewer than those used in the conventional method. By applyingthe device of this structure to the manufacture of a semiconductorappliance, as the number of mask was reduced, a manufacturing processwas simplified and a production yield was improved, whereby asemiconductor application device was offered at a more inexpensivemanufacturing cost.

In this embodiment, the anodic oxidation film was formed on the surfaceor the metal gate electrode by the anodic oxidation and athree-dimensional wiring having a grade separation was provided thereonwhich was used for a gate electrode material, and which was provided onthe surface thereof. Also, by exposing the contact part alone of asource and drain from the gate electrode and the anodic oxidation film,a feeding point is made closer to the channel and thereby thedeterioration in the frequency characteristic of the device, and theincrease in ON resistance were prevented.

In the case aluminum was used as a gate electrode material, as in thisembodiment, H₂ in the gate oxidation film was reduced into H by thecatalytic effect of aluminum, at the time of annealing process duringdevice formation, and an interfacial level density (Q_(SS)) was reduced,much compared with the case a silicon sate was used instead, and adevice characteristic was thereby improved.

Since source and drain regions of TFT were self-aligned, and the contactpart of the electrode fed to the source and drain regions was alsopositioned in a self-aligning manner, the area of the device requiredfor TFT was reduced, and the circuit integration was improved thereby.When TFT was used as an active device of the electro-optical device, theaperture ratio of liquid crystal panel was increased.

The anodic oxidation film in the vicinity of the side surface of thegate electrode was positively used, and TFT of characterized structurewas offered thereby, and the manufacture of TFT could be carried outusing the fewest possible masks of at least two pieces.

The foregoing description of preferred embodiments has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form described, andobviously many modifications and variations are possible in light of theabove teaching. The embodiments were chosen in order to explain mostclearly the principles of the invention and its practical applicationthereby to enable others in the art to utilize most effectively theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. Examples of suchmodifications are as follows.

The present invention can be applied to an electro-optical device havinga circuit shown in FIG. 23. The circuit is the same as that shown inFIG. 4 except that a capacitor is provided on the substrate andconnected to each pixel in parallel with the liquid crystal or thecorresponding pixel as shown in FIG. 23.

A nematic liquid crystal, a cholesteric liquid crystal, a ferroelectricliquid crystal or an anti-ferroelectric liquid crystal can be used for aliquid crystal layer provided between a pair of substrates in anelectro-optical device of the present invention.

1. A device having at least one liquid crystal panel, the liquid crystalpanel comprising: a first substrate having an insulating surface; asecond substrate being opposed to the first substrate; at least one thinfilm transistor being formed over the first substrate, the thin filmtransistor including at least a channel region, a gate insulating filmadjacent to the channel region and a gate electrode adjacent to thechannel region with the gate insulating film interposed therebetween; aninterlayer insulating film over the thin film transistor; a leadelectrode over the interlayer insulating film and electrically connectedto one of a source or a drain of the thin film transistor through afirst opening in the interlayer insulating film; an organic resin filmover the interlayer insulating film and the lead electrode; a pixelelectrode over the organic resin film, the pixel electrode beingelectrically connected to the lead electrode through a second opening inthe organic resin film; and an electro-optical modulating layercomprising a mixture of a liquid crystal material and a polymer resin,the electro-optical modulating layer being located between the firstsubstrate and the second substrate, wherein the first opening and thesecond opening do not overlap each other.
 2. A device according to claim1, wherein the organic resin film comprises polyimide.
 3. A deviceaccording to claim 1, wherein the pixel electrode is transparent.
 4. Adevice according to claim 1, wherein the thin film transistor is atop-gate type in which the gate electrode is located above said channelregion.
 5. A device having at least one liquid crystal panel, the liquidcrystal panel comprising: a first substrate having an insulatingsurface; a second substrate being opposed to the first substrate; atleast one semiconductor element being formed over the first substrate,the semiconductor element including at least a channel region, a gateinsulating film adjacent to the channel region and a gate electrodeadjacent to the channel region with the gate insulating film interposedtherebetween; an interlayer insulating film over the semiconductorelement; a lead electrode over the interlayer insulating film andelectrically connected to one of a source or a drain of thesemiconductor element through a first opening in the interlayerinsulating film; an organic resin film over the interlayer insulatingfilm and the lead electrode; a pixel electrode over the organic resinfilm, the pixel electrode being electrically connected to the leadelectrode through a second opening in the organic resin film; anelectro-optical modulating layer comprising a mixture of a liquidcrystal material and a polymer resin, the electro-optical modulatinglayer being located between the first substrate and the secondsubstrate, wherein the first opening and the second opening do notoverlap each other.
 6. A device according to claim 5, wherein theorganic resin film comprises polyimide.
 7. A device according to claim5, wherein the pixel electrode is transparent.
 8. A device according toclaim 5, wherein the semiconductor element is a top-gate type thin filmtransistor in which the gate electrode is located above the channelregion.
 9. A television comprising: a tuner for receiving televisionradio wave; a liquid crystal panel operationally connected to the tuner,the liquid crystal panel comprising: a first substrate having aninsulating surface; a second substrate being opposed to the firstsubstrate; at least one thin film transistor being formed over the firstsubstrate, the thin film transistor including at least a channel region,a gate insulating film adjacent to the channel region and a gateelectrode adjacent to the channel region with the gate insulating filminterposed therebetween; an interlayer insulating film over the thinfilm transistor; a lead electrode over the interlayer insulating filmand electrically connected to one of a source or a drain of the thinfilm transistor through a first opening in the interlayer insulatingfilm; an organic resin film over the interlayer insulating film and thelead electrode; a pixel electrode over the organic resin film, the pixelelectrode being electrically connected to the lead electrode through asecond opening in the organic resin film; and an electro-opticalmodulating layer comprising a mixture of a liquid crystal material and apolymer resin, the electro-optical modulating layer being locatedbetween the first substrate and the second substrate, wherein the firstopening and the second opening do not overlap each other.
 10. Atelevision according to claim 9, wherein the organic resin filmcomprises polyimide.
 11. A television according to claim 9, wherein thepixel electrode is transparent.
 12. A television according to claim 9,wherein the thin film transistor is a top-gate type in which the gateelectrode is located above the channel region.
 13. A portable computerhaving a liquid crystal panel, the liquid crystal panel comprising: afirst substrate having an insulating surface; a second substrate beingopposed to the first substrate; at least one thin film transistor beingformed over the first substrate, the thin film transistor including atleast a channel region, a gate insulating film adjacent to the channelregion and a gate electrode adjacent to the channel region with the gateinsulating film interposed therebetween; an interlaver insulating filmover the thin film transistor; a lead electrode over the interlayerinsulating film and electrically connected to one of a source or a drainof the thin film transistor through a first opening in the interlayerinsulating film; an organic resin film over the interlayer insulatingfilm and the lead electrode; a pixel electrode over the organic resinfilm, the pixel electrode being electrically connected to the leadelectrode through a second opening in the organic resin film; anelectro-optical modulating layer comprising a liquid crystal materialand a polymer resin, the electro-optical modulating layer being locatedbetween the first substrate and the second substrate, wherein the firstopening and the second opening do not overlap each other.
 14. A portablecomputer according to claim 13, wherein the organic resin film comprisespolyimide.
 15. A portable computer according to claim 13, wherein thepixel electrode is transparent.
 16. A portable computer according toclaim 13, wherein the thin film transistor is a top-gate type in whichthe gate electrode is located above the channel region.
 17. A deviceaccording to claim 1, wherein the channel region is formed in acrystalline semiconductor island.
 18. A device according to claim 5,wherein the channel region is formed in a crystalline semiconductorisland.
 19. A television according to claim 9, wherein the channelregion is formed in a crystalline semiconductor island.
 20. A portablecomputer according to claim 13, wherein the channel region is formed ina crystalline semiconductor island.
 21. A device having at least oneliquid crystal panel, the liquid crystal panel comprising: a firstsubstrate having an insulating surface; a second substrate opposed tothe first substrate; at least one thin film transistor formed over thefirst substrate, the thin film transistor including at least a channelregion, a gate insulating film adjacent to the channel region and a gateelectrode adjacent to the channel region with the gate insulating filminterposed therebetween; an interlayer insulating film over the thinfilm transistor; a lead electrode over the interlayer insulating filmand electrically connected to one of a source or a drain of the thinfilm transistor through a first opening in the interlayer insulatingfilm; a leveling film over the interlayer insulating film and the leadelectrode; a pixel electrode over the leveling film, the pixel electrodeelectrically connected to the lead electrode through a second opening inthe leveling film; an electro-optical modulating layer comprising amixture of a liquid crystal material and a polymer resin, theelectro-optical modulating layer being between the first substrate andthe second substrate, wherein the first opening and the second openingdo not overlap each other.
 22. A television comprising: a tuner forreceiving television radio wave; a liquid crystal panel operationallyconnected to the tuner, the liquid crystal panel comprising: a firstsubstrate having an insulating surface; a second substrate opposed tothe first substrate; at least one thin film transistor being formed overthe first substrate, the thin film transistor including at least achannel region, a gate insulating film adjacent to the channel regionand a gate electrode adjacent to the channel region with the gateinsulating film interposed therebetween; an interlayer insulating filmover the thin film transistor; a lead electrode over the interlayerinsulating film and electrically connected to one of a source or a drainof the thin film transistor through a first opening in the interlayerinsulating film; a leveling film over the interlayer insulating film andthe lead electrode; a pixel electrode over the leveling film, the pixelelectrode electrically connected to the lead electrode through a secondopening in the leveling film; an electro-optical modulating layercomprising a liquid crystal material and a polymer resin, theelectro-optical modulating layer being between the first substrate andthe second substrate, wherein the first opening and the second openingdo not overlap each other.
 23. A portable computer having a liquidcrystal panel, the liquid crystal panel comprising: a first substratehaving an insulating surface; a second substrate opposed to the firstsubstrate; at least one thin film transistor being formed over the firstsubstrate, the thin film transistor including at least a channel region,a gate insulating film adjacent to the channel region and a gateelectrode adjacent to the channel region with the gate insulating filminterposed therebetween; an interlayer insulating film over the thinfilm transistor; a lead electrode over the interlayer insulating filmand electrically connected to one of a source or a drain of the thinfilm transistor through a first opening in the interlaver insulatingfilm; a leveling film over the interlayer insulating film and the leadelectrode; a pixel electrode over the leveling film, the pixel electrodebeing electrically connected to the lead electrode through a secondopening in the leveling film; an electro-optical modulating layercomprising a mixture of a liquid crystal material and a polymer resin,the electro-optical modulating layer being between the first substrateand the second substrate, wherein the first opening and the secondopening do not overlap each other.
 24. A device according to claim 21,wherein the channel region is formed in a crystalline semiconductorisland.
 25. A device according to claim 21, wherein the pixel electrodeis transparent.
 26. A television according to claim 22, wherein thechannel region is formed in a crystalline semiconductor island.
 27. Atelevision according to claim 22, wherein the pixel electrode istransparent.
 28. A portable computer according to claim 23, wherein thechannel region is formed in a crystalline semiconductor island.
 29. Aportable computer according to claim 23, wherein the pixel electrode istransparent.